In U.S. Pat. No. 3,457,680, a grind stone head vibrating device for a superfinishing machine is disclosed. It presents right and left vibrators supporting the stone heads mounted on at least one pair of upper and lower round rods through bearings suspended by air. An oscillation ring is rotatably mounted and is provided with a pair of eccentric cams arranged to be equally eccentric in the opposite directions at the side of the right and left vibrators. The right and left hand vibrators are retained movably back and forth by springs pressing the vibrators towards the cams.
In U.S. Pat. No. 6,872,124, a superfinishing apparatus is disclosed. It includes a frame holding the entirety of the apparatus, a cam shaft attached to the frame so as to rotate freely, first and second eccentric cams which are attached to the cam shaft and rotate with a phase difference of 180 degrees therebetween, a first vibrator having a polygonal shape in its section which moves in a sliding manner in accordance with the rotation of the first eccentric cam, a second vibrator having a polygonal shape in its section which is disposed so as to oppose to the first vibrator through the cam shaft and moves in a sliding manner in accordance with the rotation of the second eccentric cam, bearings suspended by air for supporting the first vibrator and the second vibrator, and a superfinishing stone attached to the first vibrator or the second vibrator.
A limitation of the vibrating devices briefly described above is that the forces exerted on a mechanical object being superfinished by the grind stone head vibrating device is relatively low and accordingly limited to small mechanical objects. The load capacity of an air suspended vibrator is relatively low and prevents a compact design when higher exerted forces are needed. A compact design is a key requirement according to the second aspect of the invention. This leads to a low maximum force that may be exerted on the mechanical object to be finished via the stone. A too high force exerted on the mechanical object leads to a significantly decreased functionality of the bearings suspended by air.
Another limitation is the need of having two vibrators. This leads to overly complex and expensive vibrating devices.